Northern corn leaf spot

Northern corn leaf spot (NCLS) is primarily a concern in seed production fields where susceptible inbreds are planted. Hybrids may show some minor flecking or small lesions, but most hybrids carry adequate resistance to prevent economic losses from occurring. NCLS is favored by many of the same conditions as for NCLB and SCLB. It is primarily limited to northern Illinois, but may be found in seed fields in north central Illinois when moderate temperatures and high moisture levels occur. Spores are produced abundantly in damp weather.
Lesions of NCLS can vary depending on the race present. Race 1 lesions are tan, oval to circular with concentric zones and are commonly 1/2 inch in width and 1 inch in length. Race 2 infections are rare. Lesions are oblong, dark brown to blackish in color and 1/8 inch in width and 1 inch in length. Race 3 lesions are most common in the Corn Belt. These lesions are narrow and linear in shape, with lengths less than 1 inch and widths less than 1/8 inch. Lesion shape and size may vary with the genotype of the plant. Lesions are grayish-tan and surrounded by a pigmented border. Control measures are not usually necessary for commercial hybrids. Seed production fields can benefit from fungicide applications, especially for highly susceptible inbreds.
There are at least three known races of NCLS. Race 1 is highly pathogenic on some inbred lines; Race 2 is much less pathogenic; Race 3 is primarily a problem in seed production fields. It can also produce lesions on commercial hybrids but does no economic damage. There is also evidence that a fourth race may occur or it may be a biotype of one of the other races.